Process for rapidly obtaining steels of high purity



Patented Jan. 3t), 1940 UNITED STATES PATENT oFr-ucr.

2,188,416 PROCESS FOR RAPIDLY OBTAINING STEELS OF HIGH PURITY corporation of France.

No Drawing. Application March 13, 1939, Serial No. 261,662. In France March 30, 1938 16 Claims.

In his patent application made under Serial No. 238,881 on the 4th day of November, 1938, the applicant described a "duplex process in which steel with a low phosphorus content coming from a basic or acid converter or from another metallurgical apparatus is subjected to a short blowing in an acid converter in the presence of a substance whose oxide has a high heat of formation and which is capable of being oxidised by blowing air into the steel, for example silicon, after which if desired deoxidation of the steel is effected by any known process. Manganese may be added to the bath before the blowing.

On the one hand this process allows steel to be purified with respect to impurities which cannot be eliminated by action of a slag alone or by a single operation in the converter, and on the other hand it gives to the metal a temperature better suited for pouring and for the quality of the metal.

By the present invention it has been found that it is possible instead of using an acid converter for the final purification and reheating of the steel, to employ in a process of the kind of that mentioned above, a basic converter, with the advantages which such an aparatus shows, particularly in the case where the working up itself of the steel is effected in a Thomas converter, if as second converter is used a converter which is not contaminated with phosphorus-containing slag and the lining of which is not impregnated with such a slag. The short blowing in this second converter in the presence of a substance which is oxidisable by the air, such for example as silicon, does not then give rise to rephosphorisation of the metal which would take place if phosphorus-containing slag was present.

The purification of the steel may again be further improved, particularly with regard to sulphur, if the short blowing is efiected in the second converter in the presence of a molten or solid slag (or the constituents of a slag) rich in alkaline earth and/or alkali bases but preferably alkaline earth, and especially rich in lime and in magnesia. The proportion of this slag with respect to the bath of steel should be sufficient so that after the blowing and the corresponding formation of silica which is incorporated in the slag this latter is still basic.

In these conditions it is observed that after the short blowing, the slag, even if it has been added in the solid state, is perfectly molten and that it only contains relatively low quantities of manganese and iron oxides. The combustion by air due to the presence of the slag is practically limited to the silicon; the loss of iron and manganese is practically zero. The metal is purified, its sultphur content is reduced if the slag is employed in proportion sufficient still to be basic when the operation is finished; it is at a good temperature for pouring, it has a good micrographic purity and .good mechanical characteristics. v

Instead of adding to the steel the proportion of silicon or other analogous substance just sufiicient to give the metal the temperature necessary for casting, it is of advantage to add a proportion of silicon above that which it is desired to oxidise and not-to oxidise this excess by too long a blowing so that the final metal still contains silicon.

In at Thomas steel works as second converter or finishing converter either a special converter reserved for finishing the steel according to the invention may be used or a normal steel works converter whose lining is so little impregnated with phosphorus that no rephosphorisation is produced, for example after replacement of this lining. After one or more operations according to the invention the apparatus may be utilised .in the normal operation of refining phosphorus cast iron in order to use up its lining.

The slag may be charged either liquid, which has the advantage of only necessitating a smaller consumption of silicon to bring the metal to a good temperature, or solid. The fusability of this slag may be improved by introducing thereinto manganese oxide and iron oxide which has as a consequence the introduction of manganese and iron into the bath by the effect of the short blowing in spite of the presence of air, due to the reduction of these oxides by the silicon or equivalent substance contained in the metal.

In the case when the slag is charged in the solid state, the elements of the slag may be charged separately for example lime, alumina, fritted dolomite, manganese ore, or the whole or a part of the charge of slag may be constituted by a previously molten slag which improves fusability.

One may, for example, use liquid or solid slags from the end of an operation of refining in the Martin or electric furnace (if they contain little P205 when it is desired to produce a metal containing little phosphorus) adding to them a little lime and/or dolomite to render them more basic. This manner of procedure has the advantage of permitting the recovery of the greater part of the manganese of these slags, these being reduced by the silicon or analogous substance introduced into the bath of metal.

There may likewise be used liquid or solid slags charged with alkaline earth bases and with alumina and there may be produced thus in the basic finishing converter the operation described in the U. S. A. patent application made by the applicant under Serial No. 254,728 on the 4th day of February 1939. This process consists essentially in causing to act upon the steel containing an energetic reducing agent whose oxide has an acid character, a slag principally composed of alumina and of alkaline earth and/or alkali bases until the sla'g only contains a very small quantity of iron oxide.

In these conditions steels which are quite particularly clean from the micrographic point of view are obtained, having moreover remarkable mechanical properties, if the relative weight 01 the slag is calculated as a function of the steel treated and if one determines by experiment the value of the addition of silicon or analogous substance and the duration of the short blowing, so that the final metal still contains silicon, for example more than 0.050% and that the silica content of the slag is not too high, for example less than 30% at the end of the operation, the alumina content at this moment being at least 20%. In this case there may be used for the lining of the finishing converter for the steel, materials rich in alumina and in lime and/or in magnesia,

, for example commercial refractory cements.

One may without disadvantage-if the slag is simply an alkaline earth or alkali slag or even atthe same time an aluminous slag-add in the second converter all the desired addition elements such for example as nickel, chromium, molybdenum. Due to the action of the silicon in the presence of a slag rich in alkaline earth or alkali bases, these elements have no tendency to pass into the slag in the state of oxidesand the yield of these additions is excellent.

Moreover the presence of silicon or another analogous substance in the steel allows the alloying elements to be introduced into the steel by placing in the steel oxidic compounds of these elements, which compounds are reducible by the silicon or analogous substance added to the metal, for example calcium molybdate or vanadate if one desires to introduce respectively molybdenum or vanadium into the steel. To ensure such an operation there will be added to the steel a sufficient quantity of silicon or another analogous substance to ensure the reduction of the oxidic compound in question to the extent necessary for the introduction of the desired quantity of alloying elements into the bath of steel.

The difierent operating methods possible in the duplex operation: acid or basic converterbasic converted, according to the invention are the same as those which have been described in the first abovementioned patent application for the acid or basic converteracid converter process.

The steel dephosphorised in the basic converter or by violent intermixing with a basic fluid oxidising slag according to known processes is separated from the slag and transferred into a basic converter which is not contaminated with phosphorus-containing slag and whose lining is not impregnated with such a slag. To it is added either in the transfer ladle or in the basic converter a substance oxidisable by the air and whose oxide has a high heat of formation, for example 0.4% by weight of silicon and 5.6% of manganese. The mixture is blown for a very short time, for example 1 minute, and the steel is poured while causing it if desired to undergo a deoxidation by violent pouring from a height into an acid slag poor in iron oxide and very fluid, according to a known process. The operation may be effected by adding in the second converter a slag rich in alkaline earth or alkali bases, for example, a slag having one of the following specific initial compositions:

(1) S102: 14%; C: 54%; MgO: 10%; MnO: 10%; F'eO: 4%; NazO: 3%; fluorspar: 5%.

(2) S102: 17%; CaO: 60%; MnO: 7%; F'eO: 7%; A1203: 5%; fluorspar: 4%; this slag being in each case employed in sufflcient quantity (determined by calculation or by previous tests) so as to remain basic at the end of the operation.

Instead of a slag having a general composition such as defined above one may also utilise for the same operating method a slag principally composed of alumina and alkaline earth and/or alkali bases by operating the blowing until the slag only contains a very small quantity of iron oxide for example of the order of 1% by weight of the slag. Such a slag will have for example the following final composition:

(1) S102: 20.4%; FeO: 0.9%; A1203: 27.7%; MnO: 1.1%; 08.0: 40.8%; M80: 7.6%; T102: 1.3%.

(2) SiOz: 11.1%; FeO: 0.6%; MnO: 0.2%; AlzOa: 40%; CaO: 44.3%; MgO: 1.3%; T102: 2.6%.

It has been specified above that the second converter should not be contaminated with phosphorus-containing slag and that its lining should not be impregnated therewith. However, it should be understood that this has no absolute meaning, and that without departing from the scope of the invention the converter may be contaminated or impregnated by a small quantity of phosphorus-containing slag so long as this slag does not involve subsequent rephosphorisation oi the metal in view of the small phosphorus content which the final metal should contain.

What I claim is:

1. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphorus-containing slag and having a lining which is not substantially impregnated with phosphorus-containing slag, addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and blowing of short duration in the said basic converter.

. 2. Process for obtaining particularly pure steel at a good pouring temperature, consisting in blowing the steel in a converter, dephosphorising the steel, transferring the steel into a basic converter not substantially contaminated with phosphorus-containing slag and having a lining not substantially impregnated by phosphorus-containing slag, adding to the steel a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and efiecting a blowing of short duration in the said basic converter.

3. Process for obtaining particularly pure steel at a good pouring temperature, consisting in blowing the steel in a basic converter, dephosphorising the steel in the said basic converter, transferring the steel into a second basic converter not substantially contaminated by phosphorus-containing slag and having a lining not substantially impregnated with phosphoruscontaining slag, adding to the steela substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and effecting a blowing of short duration in the second basic converter.

4. Process for obtaining particularly pure steel at a good pouring temperature, consisting in blowing the steel in a basic converter, dephosphorising the steel outside the said basic converter, transferring the steel into a second basic converter not substantially contaminated by phosphorus-containing slag and having a lining not substantially impregnated with phosphorus-containing slag, adding to the steel a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and in effecting a blowing of short duration in the second basic converter.

5. Process for obtaining particularly pure steel at a good pouring temperature, consisting in blowing the steel in an acid converter, dephosphorising the steel outside the said acid converter, transferring the steel into a basic converter not substantially contaminated with phorphorus-containing slag and having a lining not substantially impregnated by prosphoruscontaining slag; adding to the steel a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and effecting a blowing of short duration in the said basic converter.

6. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphorus-containing slag and having a lining which is not substantially impregnated with phosphorus-containing slag with addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation andwhich is in a quantity which is not prejudicial in the steel at the end of the operation, and blowing of short duration in the said basic converter,.

and deoxidation of this steel.

'7. Process for obtaining particularly pure steel at good pouring temperature, comprising the' phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, with addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, addition of manganese and blowing for a short time "in the same basic converter.

8. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontainin'g slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of a subv stance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and blowing of short duration in the said basic converter, the said blowing being effected in the presence of a quantity of strongly, basic slag suflicient so that after blowing the slag is still basic.

9. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and blowing of short duration in the said basic converter, the said blowing being effected in the presence of a slag rich in alumina and in bases belonging to the group constituted bythe alkaline earth and alkali bases.

10. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, this substance being added in quantity greater than that which is necessary to impart to the metal a suitable temperature for pouring, and blowing of short duration in the said basic converter.

11. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, and blowing of short duration in the said basic converter, and introduction into the steel during this short blowing of alloying elements.

12. Process for obtaining particularly pure steel at good pouring temperature, comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of a substance readily oxidisable by air, whose oxide has an elevated heat of formation and which is in a quantity which is not prejudicial in the steel at the end of the operation, blowing of short duration in the said basic converter, and introduction into the steel during this short blowing of oxidic compounds of elements to be alloyed with the steel, and which are reducible by the substance whose oxide has an elevated heat of formation.

13. Process for obtaining particularly pure steel at good pouring temperature comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphorussteel at a good pouring temperature, consisting in blowing the steel in an acid converter, dephosphorising the steel outside the said acid converter, transferring the steel into a basic converter not substantially contaminated with phosphorus-containing slag and having a lining not substantially impregnated by phosphoruscontaining slag, adding silicon to the steel and eflecting a blowing of short duration in thesaid V basic converter.

16. Process for obtaining particularly pure steel at good pouring temperature comprising the phases of dephosphorisation of the steel, transfer of the steel into a basic converter which is not substantially contaminated by phosphoruscontaining slag and having a lining which is not substantially impregnated with phosphoruscontaining slag, addition to the steel of at least one element of the group consisting of manganese and silicon, and blowing of short duration in the said basic converter.

RENE PERRIN. 

